The present invention relates to a lens unit, and in particular, to a technology for operating smoothly a movable lens frame provided in the lens unit.
In recent years, a movable lens frame having therein a movable lens that moves in the direction of an optical axis is provided in a lens unit employed in a video camera, a still camera and a digital still camera, and the movable lens frame has been required to move more smoothly. As a lens unit like this, there is known a lens unit which has two movable lens frames, for example, and slides on two guide shafts.
On the other hand, as a structure of the lens unit, there have been known a type wherein a lens and others are incorporated in the direction that is in parallel with an optical axis of a lens and a type of a box body wherein a lens and others are mainly incorporated in the direction perpendicular to an optical axis of a lens, which is different from a conventional type.
Now, referring to the drawings, there will be explained an example of a conventional way for a type to incorporate mainly in the direction perpendicular to an optical axis of a lens, for a lens unit that has two movable lens frames and slides on two guide shafts, which differs from a conventional type.
FIG. 13 is a side sectional view of the state of telephoto end showing a structure of a lens unit in a conventional example, and FIG. 14(a) shows sectional view taken on line Axe2x80x94A in FIG. 13, FIG. 14(b) shows sectional view taken on line Bxe2x80x94B in FIG. 13 and FIG. 14(c) shows sectional view taken on line Dxe2x80x94D in FIG. 13.
Structures of a lens unit in FIG. 13 and FIG. 14 will be explained. The numeral 19 is a box-shaped box body, and box body 19 has an opening section on its top in FIG. 14(a). Further, front fixed lens frame 51 described later is fixed on the side of the box body 19 closer to a subject on an optical axis of a lens. Further, inside the box body 19, there are provided positioning grooves 19a and 19b, groove 19a positioning both ends of the first guide shaft 31 and groove 19b positioning both ends of the second guide shaft 32.
The numeral 31 is a first guide shaft provided inside the box body 19 to extend to be in parallel with an optical axis, and both ends of the first guide shaft 31 are positioned by the positioning groove 19a. The numeral 32 is a second guide shaft provided inside the box body to extend to be in parallel with an optical axis, and both ends of the second guide shaft 32 are positioned by the positioning groove 19b. 
The numeral 51 is a front fixed lens frame having lens L1, and it is fixed on the box body 19 directly. The numeral 69 is a first movable lens frame having lens L2, and the first movable lens frame 69 moves to be in parallel with an optical axis. Further, on the first movable lens frame 69, there are formed guide bush 69a and rotation-stopper section 69d. On the guide bush section 69a, there are provided hole 69b and hole 69c through which the first guide shaft 31 slides. On rotation-stopper section 69d, there is provided an elongated hole through which the second guide shaft 32 slides.
The numeral 79 is a fixed lens frame that is arranged to be in parallel with an optical axis between the first movable lens frame 69 and second movable lens frame 89, and has lens L3. The fixed lens frame 79 has therein hole 79a, elongated hole 79b, protruded portion 79c and protruded portion 79d. The hole 79a engages with the first guide shaft 31, and the elongated hole 79b is engaged with the second guide shaft 32. Positioning in the direction perpendicular to an optical axis is conducted by the first guide shaft 31 and the second guide shaft 32. Protruded portion 79c and protruded portion 79d engage respectively with grooves provided on box body 19 to conduct positioning in the optical axis direction. Incidentally, the fixed lens frame 79 may also be positioned directly on the box body 19 to be held thereon.
The numeral 89 represents a second movable lens frame having lens L4, and the second movable lens frame 89 moves to be in parallel with an optical axis. Further, the second movable lens frame 81 has guide bush section 89a and rotation-stopper section 89d. On the guide bush section 89a, there are provided hole 89b and hole 89c through which the second guide shaft 32 slides. On rotation-stopper section 69d, there is provided an elongated hole through which the first guide shaft 31 slides.
The symbol 49A is a guide shaft holding member, and guide shaft holding member 49A has claw section 49Aa, claw section 49Ab, holding section 49Ad and holding section 49Ae, as shown in FIG. 14(a). Each of the holding section 49Ad and holding section 49Ae holds one end of each of the first guide shaft 31 positioned by positioning groove 49a on the box body 11 and the second guide shaft 32 positioned by positioning groove 49b. Further, claw section 49Aa and claw section 49Ab engage with grooves on the box body 11 to fix the guide shaft holding member 49A on the box body 11.
The symbol 49B is a guide shaft holding member, and guide shaft holding member 49B is the same as the guide shaft holding member 49A stated above in terms of function, thereby explanation of the guide shaft holding member 49B will be omitted. Further, filter 21 and CCD 22 are fixed on the rear side of the box body 11.
Motor 25 that drives the first movable lens frame 69 is fixed on the box body 19 at the position opposite to the opening on the box body, and the first movable lens frame 69 is connected with the motor 25 by a connecting member mounted on the first movable lens frame 69. The foregoing is the same for the second movable lens frame 89, and an unillustrated motor is fixed on the box body 19 at the position opposite to the opening on the box body 19, and the second movable lens frame 89 is connected with the unillustrated motor by an unillutrated connecting member mounted on the second movable lens frame 89. Sensor 24 for the initial position of the first movable lens frame 69 is fixed on the same side of the box body as for the motor 25, as shown in FIG. 14(b), and an unillustrated sensor for the initial position of the second movable lens frame 89 is fixed in the same manner. An opening section of the box body 19 is covered by an unillustrated cover so that the inside of the box body is in the state of a dark box.
Now, a movement from a wide-angle end to a telephoto end will be explained. When the motor 25 drives, guide bush section 69a of the first movable lens frame 69 slides on the first guide shaft 31. Incidentally, rotation-stopper section 69d of the first movable lens frame 69 slides on the second guide shaft 32.
The longer, length X in the optical axis direction between hole 69b and hole 69c on guide bush section 69a of the first movable lens frame 69 sliding on the first guide shaft 31 is, the more stable, the operation in the course of movement of the first movable lens frame 69 is. It is therefore preferable to design the aforesaid length X of the guide bush section 69a to be long as far as possible.
However, guide bush length X of guide bush section 69a in the optical axis direction of the first movable lens frame 69 cannot be long to interfere, for example, the rotation-stopper section 89d of the second movable lens frame 89 and the protruded portion 79d of fixed lens 78. When guide bush length X of the guide bush section 69a is short, sliding friction between the first guide shaft 31 and the guide bush section 69a deteriorates smoothness of sliding. Further, when the first movable lens frame is used for variable power of a zoom lens, for example, if sliding is not stable, there is easily caused a problem of the so-called camera shake.
The invention has been attained in view of the problems mentioned above, and its object is to provide a lens unit represented by a box type lens unit wherein a movable lens frame can be slid smoothly.
As another problem, there is a problem that harmful rays entering the optical system from the outside tend to be reflected on a guide shaft near an optical axis of an optical path to be harmful light, and a lens unit tends to be large in size if the first guide shaft is made to be more distant from an optical axis.
Therefore, another object of the invention is to provide a lens unit of a box type wherein a movable lens frame can be slid smoothly and internal reflection is less.
The objects stated above can be attained by either one of the following structures.
(1) A lens unit having an optical axis, an object side through which light incomes from an object, and an image side from which the light outgoes toward an image plane, comprises a box body having an opening at one side other than the object side and the image side;
a first movable lens frame provided in the box body and having a lens;
a second movable lens frame provided in the box body at a position closer to the image side than the first movable lens frame and having a lens; and
a first guide shaft, a second guide shaft and a third guide shaft each of which is provided in the box body and arranged to be parallel to the optical axis,
wherein the first movable lens frame has a first hole portion to slide on the first guide shaft and a second hole portion to slide on the second guide shaft and the second movable lens frame has a first hole portion and a second hole portion one of which slides on the third shaft, and
wherein a length of the first hole portion of the first movable lens frame along the optical axis is longer than that of the second hole portion of the first movable lens frame along the optical axis, and a length of the first hole portion of the second movable lens frame along the optical axis is longer than that of the second hole portion of the second movable lens frame along the optical axis.
(2) A video camera comprising the lens unit of (1).
(3) A still camera comprising the lens unit of (1).
Structure 2-1
A lens unit that is provided, in its inside of a box-shaped box body having an opening on its one side, with at least a first movable lens frame having a lens and a second movable lens frame having another lens in this order from a subject, wherein there are provided a first guide shaft, a second guide shaft and a third guide shaft which are provided inside the box body and extend to be in parallel with an optical axis, the first movable lens frame stated above having thereon a guide bush section that slides on the first guide shaft and a rotation-stopper section that slides on the second guide shaft, and the second movable lens frame stated above having thereon a guide bush section that slides on the second guide shaft and a rotation-stopper section that slides on the third guide shaft.
Structure 2-2
The lens unit according to the Structure 2-1, wherein there is provided, in the inside of the box body, a positioning groove that positions both ends of at least one guide shaft among the first, second and third guide shafts.
Structure 2-3
The lens unit according to the Structure 2-1 or the Structure 2-2, wherein there is provided a guide shaft holding member that holds both ends of the guide shaft positioned by the positioning groove stated above.
Structure 2-4
The lens unit according to the Structure 2-3, wherein the guide shaft holding member positions and holds both ends of at least one guide shaft among the first, second and third guide shafts, on the box body.
Structure 2-5
The lens unit according to the Structures 2-1, 2-2, 2-3 or 2-4, wherein a fixed lens frame having a fixed lens is provided between the first movable lens frame and the second movable lens frame.
Structure 2-6
The lens unit according to the Structure 2-5, wherein the fixed lens frame is positioned in the direction perpendicular to an optical axis by the second guide shaft and the first guide shaft or by the second guide shaft and the third guide shaft.
Structure 2-7
The lens unit according to the Structure 2-5 or the Structure 2-6, wherein the fixed lens frame is positioned and held by the box body.
Structure 2-8
A lens unit that is provided, in its inside of a box-shaped box body having an opening on its one side, with at least a first movable lens frame having a lens and a second movable lens frame having another lens in this order from a subject, wherein there are provided a first guide shaft, a second guide shaft, a third guide shaft and a fourth guide shaft all being in parallel with an optical axis which are provided inside the box body and extend to be in parallel with an optical axis, the first movable lens frame stated above having thereon a guide bush section that slides on the first guide shaft and a rotation-stopper section that slides on the second guide shaft, and the second movable lens frame stated above having thereon a guide bush section that slides on the third guide shaft and a rotation-stopper section that slides on the fourth guide shaft, or having thereon a guide bush section that slides on the fourth guide shaft and a rotation-stopper section that slides on the third guide shaft.
Structure 2-9
The lens unit according to the Structure 2-8, wherein there is provided a positioning groove that positions both ends of at least one guide shaft among the first, second, third and fourth guide shafts.
Structure 2-10
The lens unit according to the Structure 2-9, wherein there is provided a guide shaft holding member that holds both ends of at least one of the first, second, third and fourth guide shafts.
Structure 2-11
The lens unit according to the Structure 2-10, wherein the guide shaft holding member positions and holds both ends of at least one guide shaft among the first, second, third and fourth guide shafts, on the box body.
Structure 2-12
The lens unit according to the Structures 2-7, 2-8, 2-9 or 2-10, wherein a fixed lens frame having a fixed lens is provided between the first movable lens frame and the second movable lens frame.
Structure 2-13
The lens unit according to the Structure 2-12, wherein the fixed lens frame is positioned in the direction perpendicular to an optical axis by either one of a combination of the first guide shaft and the second guide shaft, a combination of the first guide shaft and the fourth guide shaft, a combination of the second guide shaft and the third guide shaft and a combination of the third guide shaft and the fourth guide shaft.
Structure 2-14
The lens unit according to the Structure 2-12 or the Structure 2-13, wherein the fixed lens frame is positioned and held on the box body.
Structure 3-1
A lens unit comprising a box body having on its one side an opening portion, a first guide shaft that is provided to extend to be in parallel with an optical axis in the inside of the box body and is fixed with its both ends positioned and fixed on the box body, a second guide shaft that is provided to extend to be in parallel with an optical axis in the inside of the box body and is fixed with its one end positioned and fixed on the box body, a first guide shaft holding member that fixes one end of the first guide shaft on the front end of the box body, a second guide shaft holding member that fixes the other end of the first guide shaft and one end of the second guide shaft on the rear end of the box body, a first movable lens frame on which a bush section that slides on the first guide shaft is formed and a movable lens is provided, and a fixed lens frame having a fixed lens which positions and fixes the other end of the second guide shaft and is fixed on the box body.
Structure 3-2
The lens unit according to the Structure 3-1, wherein the box body has a positioning groove that positions both ends of the first guide shaft and one end of the second guide shaft in the direction perpendicular to the optical axis, both ends of the first guide shaft are positioned in the positioning groove, one end of the second guide shaft is positioned in the positioning groove, the first guide shaft holding member holds one end of the first guide shaft that is in the positioning groove, and fixes it on the box body, and the second guide shaft holding member holds the other end of the first guide shaft that is in the positioning groove and one end of the second guide shaft that is in the positioning groove, and fixes them on the box body.
Structure 3-3
The lens unit according to the Structure 3-1, wherein the box body has a positioning groove that positions both ends of the first guide shaft and one end of the second guide in the direction perpendicular to the optical axis, both ends of the first guide shaft are positioned in the positioning groove, one end of the second guide shaft is positioned on the box body, the first guide shaft holding member holds one end of the first guide shaft that is in the positioning groove and fixes it on the box body, and the second guide shaft holding member holds the other end of the first guide shaft that is in the positioning groove and fixes one end of the second guide shaft.
Structure 3-4
A lens unit comprising a box body having on its one side an opening portion, a first guide shaft that is provided to extend to be in parallel with an optical axis in the inside of the box body and is fixed with its both ends positioned and fixed on the box body, a third guide shaft that is provided to extend to be in parallel with an optical axis in the inside of the box body and is fixed with its one end positioned and fixed on the box body, a second guide shaft that is provided to extend to be in parallel with an optical axis in the inside of the box body and is fixed with its both ends positioned and fixed on the box body, a first guide shaft holding member that fixes one end of each of the first guide shaft and the second guide shaft on the front end of the box body, a third guide shaft holding member that fixes the other end of each of the first guide shaft and the second guide shaft and one end of the third guide shaft on the rear end of the box body, a first movable lens frame on which a bush section that slides on the first guide shaft is formed, a rotation-stopping section that slides on the second guide shaft is formed, and a movable lens is provided, and a fixed lens frame having a fixed lens which positions and fixes the other end of the third guide shaft and is fixed on the box body.
Structure 3-5
The lens unit according to the Structure 3-4, wherein the box body has a positioning groove that positions both ends of each of the first guide shaft and the second guide shaft and one end of the third guide shaft in the direction perpendicular to the optical axis, both ends of the first guide shaft are positioned in the positioning groove, one end of the third guide shaft is positioned in the positioning groove, both ends of the second guide shaft are positioned in the positioning groove, the first guide shaft holding member holds one end of each of the first guide shaft and the second guide shaft which are in the positioning groove, and fixes it on the box body, and the third guide shaft holding member holds the other end of each of the first guide shaft and the second guide shaft which are in the positioning groove and one end of the third guide shaft that is in the positioning groove, and fixes them on the box body.
Structure 3-6
The lens unit according to the Structure 3-4, wherein the box body has a positioning groove that positions both ends of each of the first guide shaft and the second guide shaft, both ends of the first guide shaft are positioned in the positioning groove, one end of the third guide shaft is positioned in the positioning groove, the first guide shaft holding member holds the aforesaid one end of each of the first guide shaft and the second guide shaft which are in the positioning groove, and fixes it on the box body, and the third guide shaft holding member holds the other end of each of the first guide shaft and the second guide shaft which are in the positioning groove and fixes one end of the third guide shaft.
Structure 3-7
The lens unit according to either one of the Structures 3-1-3-6, wherein there is provided a second movable lens frame wherein a bush section that slides on the third guide shaft and a rotation-stopping section are formed and a movable lens is provided.
Structure 3-8
The lens unit according to either one of the Structures 3-1-3-7, wherein the box body has an opening section on it side facing in the direction perpendicular to an optical axis.